Most of the chemotherapeutic agents presently used to treat breast cancers primarily target dividing cells, with subsequent radiation treatments killing the remaining cells at the primary site. Unfortunately, patients with more aggressive breast tumors often exhibit resistance to chemotherapy and radiation treatments. These resistant cells continue to grow and then metastasize to the bone and other sites in the body. We propose here to develop a novel therapeutic strategy using neural stem cells (NSCs) as a delivery vehicle for Soluble Secreted TWIST lnhibitors (SSTIs) to target resistant tumor site on cells that have metastasized to bone and other tissue sites in a rodent model. Since our preliminary data suggest that interfering with Wnt signaling and transcription factor genes, such as TWIST, can induce breast tumor cells to differentiate or apoptos in vitro, and thus may reduce their tumorigenic properties of invasion, angiogenesis and metastasis in vivo. We propose strategies to identify and evaluate potential SSTIs designed to specifically inhibit TWIST in breast tumor tissues and cell models. NSCs, by virtue of their inherent migratory and tumor-tropic properties, represent a novel and potentially powerful approach for the treatment of invasive tumors. We will first determine time course and distribution pattern of intravascularly administered NSCs in rodents with established breast carcinoma and metastases. We will then genetically modify NSCs to stably over-express SSTI-NSCs (SSTI-NSCs). Therapeutic efficacy will be demonstrated in vivo by tail vein injected SSTI-NSCs in a syngeneic metastatic breast tumor model. Breast tumor cells will be engineered to express the Firefly Luciferase bioluminescent reporter gene. This will allow weekly, quantitative, in vivo monitoring of tumor burden by Xenogen imaging, as animals are followed for long term survival. Finally, we will demonstrate the ability of peripherally injected SSTI producing NSCs to target human mammary tumors and metastases in a nude mouse model, and affect a therapeutic response through TWIST inhibition. The success of these animal trials could have significant implications for future clinical application for advanced human breast cancer.